Thorny problems: how can I stop rose black spot?

One last trick you might want to try: Uncle Toms Rose Tonic (see naturalgardensolutions.com for stockists, which include the RHS at Wisley). Despite its clunky-sounding name, this highly effective foliar feed also helps to control fungal diseases, and can dramatically improve the vigour of your rose bushes generally. Healthy plants fight off diseases far better than those that are struggling.

Help for honeysuckle

Do shrubs just run out of steam? I recently saw a winter-flowering honeysuckle absolutely covered in beautifully scented flowers in Bedgebury Pinetum in Kent. I have a similar seven-year-old shrub in my own garden a few miles away, but despite annual pruning and feeding, mine has never flowered profusely and seems to be going downhill year by year.

Carolyn Lovell, via email

This could be simply a question of variety. Your shrub may be Lonicera fragrantissima, while the one you admired may well have been Lonicera x purpusii Winter Beauty, which is generally regarded as superior. It is altogether more compact than

L. fragrantissima, more floriferous and with what can only be described as much more oomph.

You could, however, have been over-pruning your shrub, or pruning it too late. You have to be quick off the mark with winter-flowering shrubs, cutting them back the moment the flowers have faded so that new growth has time to ripen sufficiently to carry flowers the following year. If you prune late and are a bit brutal into the bargain (to keep it in bounds in the case of L. fragrantissima this is a temptation, since it is a lanky, unattractive thing, in my view), the new growth doesnt have time to ripen.

Do shrubs run out of steam? Yes, they must, eventually. But the majority of garden shrubs, if given optimum growing conditions and pruned sensibly every year, with some old growth removed to encourage the production of new, will truck on happily for years and (as an expression that I use far too often) goes, see us out.

Wet lawn weeds

Not one but two weeds of wet ground have unsurprisingly reared their ugly heads this week. Emailer Terry Smith complains about borders invaded by rampant sheeps sorrel (Rumex acetosella), a small-leafed, russet-flowered sorrel that spreads via vigorous rhizomes. He wonders how to tackle it. I had this one embedded in and around an old Victorian rockery, so I know how he feels. I defeated it (more or less) by resorting to that well-known gardeners exercise, a combination of angry ripping and timely daubing with glyphosate when what survived the angry ripping produced enough leaf to treat. The trouble with rhizomatous weeds like this is that every bit that remains after digging/ripping seems to grow with renewed vigour. Sheeps sorrel is a weed of boggy, acid soil, so improving drainage and upping the alkalinity of soil by liming (with ground chalk or ground limestone) may help.

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Thorny problems: how can I stop rose black spot?